Bohemian knotweed

Fallopia japonicus x bohemica

Bohemian knotweed (Fallopia japonicus x bohemica) is a hybrid of Japanese knotweed (Fallopia japonica) and Giant knotweed (Fallopia sachalinensis). Its features are intermediate between those of the parent species.

The leaves of Bohemian knot weed and side by side are the leaves of Giant knotweed, Bohemian knotweed, Japanese knotweed, Himalayan knotweed.

The leaves are larger than Japanese knotweed but smaller than Giant knotweed (up to 23cm long). Leaves can vary in shape from square-ended to heart-shaped and both variations can appear on the same plant. Bohemian knotweed does not grow as tall as Giant knotweed but, like all knotweeds, it forms dense stands that exclude other plant species and reduce biodiversity.

Unlike the parental Japanese knotweed, Bohemian knotweed produces viable seeds in the UK and Ireland. This increases its invasive potential. It can also spread from cuttings and fragments. Knotweeds prefer moist, damp soil with lots of sunshine but will also tolerate most environmental conditions. They can often be found in waste ground and along river banks.

Much Bohemian knotweed in Ireland and the UK may well be mis-identified as Japanese knotweed and it is considered to be quite widely distributed in Ireland.